games

This is most likely caused by CPU or RAM(s).
Try with a known good CPU and then RAM.

Does this problem happen with any other programs?

If no, make sure that the driver for the video card supports the version of DirectX that you have.
Many older cards do not have drivers that support DirectX 8 or 9.

If yes, you have a corrupted Windows installation. Any number of causes, including remnants from removed software and device drivers.

If the PC is over 2 years old, I would seriously consider performing a fresh install of Windows.

Back up your data files and settings.
Download the latest device drivers.
Boot from a startup disk.
Run fdisk and delete at least the Primary DOS partition.
Re-boot and partition the drive as desired.
Re-boot and format at least the C: drive
Insert the Windows CD, and run setup.

Install device drivers in the following order:
Motherboard / system drivers
DirectX (Latest version supported by the video card driver)
Video card driver
Modem and network drivers
Sound card driver
Printer and other external devices.

Boot into safe mode, and run scandisk and defrag.

Connect to the internet, and update Windows.

Run scandisk and defrag again.

Install ONLY the software and utilities that you actively use.

Chas

This might sound like a stupid answer, but you are probably hitting the windows key...most games running full screen will then minimize to the task bar...
Have a think....does it happen when you play games where you use CTRL or ALT as buttons and tap away frantically...?

i had that problem before.

it could be due to some program suddently started to run, or some internet advertisment that pop up while you are playing games.

check that also.

i had something like that problem before.

it could be due to some program suddently started to run, or some internet advertisment that pop up while you are playing games.

check that also.